feat : Exercise4

src/main/java/org/nhnacademy/minju/Exercise4.java

@@ -0,0 +1,142 @@
+package org.nhnacademy.minju;
+
+import java.util.Scanner;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * .이진트리의 항목을 인쇄
+ * 스택이나 큐를 사용할 경우 비재귀 서브루틴을 사용하여 인쇄할 수 있다
+ * TreeNodes
+ */
+public class Exercise4 {
+
+
+    private static final Logger logger = LoggerFactory.getLogger(Exercise4.class);
+
+    /**
+     * .add root node to empty queue
+     * get node from the queue
+     * print the item in the node
+     * treeNode have left, right
+     */
+    public static void exercise4() {
+        Scanner scanner = new Scanner(System.in);
+        TreeNode treeNode = new TreeNode();
+        String input;
+
+        logger.info("Enter items, or Enter Empty Line to Finish Input : ");
+        while (!(input = scanner.nextLine()).isEmpty()) {
+            treeNode.insertItem(input);
+        }
+        treeNode.inorderTraversal();
+    }
+}
+
+class TreeNode {
+    private static final Logger logger = LoggerFactory.getLogger(Exercise4.class);
+
+    String item;
+    TreeNode left;
+    TreeNode right;
+
+    public TreeNode(String newItem) {
+        item = newItem;
+    }
+
+    public TreeNode() {
+
+    }
+
+    private TreeNode root;
+
+    public void insertItem(String newItem) {
+        if (root == null) {
+            root = new TreeNode(newItem);
+            return;
+        }
+        // not empty
+        TreeNode runner = root;
+        while (true) {
+            if (newItem.compareTo(runner.item) < 0) { // string
+                if (runner.left == null) {
+                    runner.left = new TreeNode(newItem);
+                    return;
+                }
+                runner = runner.left;
+            } else {
+                if (runner.right == null) {
+                    runner.right = new TreeNode(newItem);
+                    return;
+                }
+                runner = runner.right;
+            }
+        }
+    }
+
+    void inorderTraversal() {
+        if (root == null) {
+            return;
+        }
+        Queue queue = new Queue();
+        queue.enqueue(root);
+        while (!queue.isEmpty()) {
+            TreeNode node = queue.dequeue();
+            if (node.left != null) {
+                queue.enqueue(node.left);
+            }
+            logger.info("{}", node.item);
+            if (node.right != null) {
+                queue.enqueue(node.right);
+            }
+        }
+    }
+
+}
+
+class Queue {
+    private static class Node {
+        TreeNode item;
+        Node next;
+    }
+
+    private Node head = null;
+    private Node tail = null;
+
+    /**
+     * queue에 추가
+     */
+    void enqueue(TreeNode tree) {
+        Node node = new Node();
+        node.item = tree;
+        if (head == null) {
+            head = node;
+            tail = node;
+            return;
+        }
+        tail.next = node;
+        tail = node;
+    }
+
+    /**
+     * queue의 첫 번째 아이템을 리턴
+     * 큐가 비어있으면 throw Exception
+     */
+    TreeNode dequeue() {
+        if (head == null) {
+            throw new IllegalStateException("can't dequeue from empty queue");
+        }
+
+        TreeNode first = head.item;
+        head = head.next; // 2->1
+        if (head == null) {
+            // empty
+            tail = null;
+        }
+        return first;
+    }
+
+    boolean isEmpty() {
+        return (head == null);
+    }
+}